Have to agree with all the others, tell the newbie to nix the rayon for quilting, it is too weak and is often not colorfast. Especially for kids quilts which will take a lot of "hard love'n" and laundering. Also tell her to avoid serger thread for strength reasons but I have heard many LAers run it with no problem I would prefer to err on the side of caution.

If she wants pretty, shiny thread go with any of the beautiful polyester embroidery/longarming threads that are on the market like Filtec Glide, Superior Magnifico, Metro Embroidery (although made in China and I try to support American made whenever possible)

As far as bobbin, many do use the same color at least but not always the same thread. I know many quilters who will run Superior Bottom Line in the bobbin and be running a different thread, in the same color family on top. I regularly run magnaglide bobbins in the bottom and Glide in the top but have also run King Tut, Invisifil, YLI Cotton, or even Connecting Threads cotton in top.

I prefer to use the same color family in my bobbin but I won't hesitate to go different if that is what the client wants. Using different colors in top and bobbin does help you get better at adjusting your tension.

or go absolutely BONKERS trying to get it the tension right!!!!!! ROL ROL I finally gave up years ago....but I know some longarmers are able to do it without problems. :) Some have the talent, some of us don't.

I always use different threads from top and bottom....My machine loves 70 weight superior threads bottom line, or so fine.........for the bottom thread. The top thread is any kind of 40-50 weight thread.. I will tell you, that the rayon thread isn't a great idea. I love signature and marathon thread on the top. Using the same colors is helpful but sometimes isn't available. Try to get as close as possible. Hope this helps

I should mention that there is a rule-of-thumb out there for longarmers, that it is best to use a "grippy" thread such as cotton with a "slippy" thread such as polyester. The grippy thread helps lock the slippy thread in place. This is probably why using something like Bottom Line (fine poly) in the bobbin with King Tut (heavier cotton) on top seems to work well.