I just got my own Great G'ma's stash yesterday! She had a beautiful appliqued crib quilt top that was never finished. I've decided that I'm not touching it until I can hand quilt. My biggest issue with this top is that it's a baby girl crib quilt...and I don't have any baby girls in the family coming...and possibly won't get any. My own daughter is only 5, and this top is already 30 years old. I don't want it to leave the family, it was passed mother to daughter to me unfinished...but assuming my daughter someday has a daughter, this beautiful quilt won't get any use for 20 more years (I hope it's that long before she starts having babies!). It makes me sad that it will have to wait so long for love.
She also had a huge stack of squares cut. I plan to use those squares and make big scrappy pinwheel quilt.
As for what you have - if you really want to finish what she started in her style, *I* would wait until I felt my skill level was there to do it justice. But I don't feel, in any way, that "doing your thing" with them would be an *injustice* to your great grandmother's fabrics. Nor do I think that you should feel obligated to use fabrics that you just don't like. Maybe you could use those to make something to give back to your mom. I bet she'd love it knowing that you and your great grandmother came together, in way, to make something for her.