Your practice dress could become the slip for the final dress. Yes you really can make it. The 'Simplicity' christening pattern is good but how old will the baby be when it get baptised? Babies gain weight really fast and change size. Practice on something from your stash.
Hope to see a photo of your practice dress and of course "The Final Production".

Good luck! I made a simple christening dress for my daughter 30 yrs. ago. I used a white fabric with and eyelet edge. It was very simple. I agree it will be a family heirloom. Lot's of good ideas here on the board. Just do what's comfortable for you.

as long as you add some pleats and lace, any fabric will look great. Good luck!! I watch this ladies show once in awhile. she does great dresses, blouses, etc. http://www.marthapullen.com/

I love love love to make little girl dresses. The worst part is all the gathering. It can be a pain in the neck, but it can also hide a LOT of not so perfect seams, etc. If something doesn't come out just the way you expected, hide it with another pc of lace. I have made a few christening dresses. They don't have to be made from expensive material. White cotton with a layer of lace or tulle. There is actually a tulle like fabric that I have used. Got it at Joannes, it has a shiney oyster shell finish. Long, lots of ruffles and lace. Make your own lace from the tulle, yea, I know, more gathering. I actually have a box of satin in all the colors. Yellow, green, blue, pink, I think 7 in all. They are the bridesmaids dresses for my DD's wedding that was cancelled at the last minute. There is a lot of that clamshell tulle, as well. Is she set on white? I would happily give you some of this fabric if it would work. I bought a bolt and a half of the overlay. We were going to use it for decorations. OK, I am rambling. I get excited. PM if you are interested.

I am in the process of making a second christening dress for my newest grandchild. The baptism was put off due to the availability of both godparents. One is a merchant marine and the other lives out of state. The original dress is for a newborn. The one I'm making now is a medium. The baby is now 6 months old. I make the christening outfits usually for a shower gift. They are 100% cotton. I don't play around with jewels as they could possible scratch a baby. I do use washable lace or trim. I'd give your daughter a choice, a simple dress you are comfortable that you can do successfully or she could possibly purchase one. Some of the Irish shops sell beautiful linen dresses. Don"t drive yourself crazy about it. You won't enjoy the process. Pick a simple one. Watch the Missouri Star quilt video demonstrating a skirt for little girls. She was a stage clothing seamstress and shows how to gather in a really simple method. Try it out first on a scrap. I'm going to do that this pm. I also suggest that you complete the top and then attach the skirt which has whatever trim you want to use already on it. It makes the whole process so much simpler. Good luck!

People know people. Ask in your area. Talk to your neighbors. I'm sure there is someone who could help you. Christening gowns can be passed on down through the family. Not sure what your date for the Christening is but hope you have more than just a couple of days. My neighbor took a couple little dresses apart added some beading and then just lengthened the skirt by about 20 + inches. Did the same for grandson just made it look more like a white papal gown.

I made a wedding dress one time and found 40 yr old scalloped Italian lace. It could only be cut in one direction so the scallops were on the bottom at the hem and the sleeves hem. The lace was $40/yd but they had it the in the store for so long they sold it to me at a discount = $20/yd. Still it was very intimidating to cut it...but the gown turned out beautiful. :thumbup:

Have you thought of visiting thrift shops and picking up a slightly used wedding gown? Lots of beading, satin, etc. I've made a lot of christening gowns using leftovers from wedding dresses.

For an acquaintance, I've made two Baptismal Gowns from the mothers-to-be First Communion dresses. Left the skirt length as it was; but used a pattern to cut the bodice; left it as original as possible, like the button down back, resized the fancy sleeves or lacey yokes.. Lots of work, but turned out great. Have one more to do once the daughter gets married and pregnant!!

Here is the dress
 

Looks like lots of improvisation and lots of $$$ for lace and beading.....and lots of time at the sewing machine!