If you want something nice that will last forever try Garden Smiles! The artist is based here in NWOH and the pieces are beautiful! I have many pieces (I get some as seconds at the shop) and often give them as gifts for weddings, birthdays, you name it. Some of the smaller pieces are not too expensive and they will ship them for you. Your mom can put the piece up in the house, on a wall, on a shelf, anywhere, or in the garden where it can stay all year - I leave mine out in the winter every year.
If your mom has a collection of something, they probably have a piece that would fit in. My neighbor has bunnies so we gave her this one year:
Bunny mini it is utterly adorable sitting on a shelf.
This would make a nice Mother's Day gift:
Thank you
or this one:
Love
I know that I am getting a green man for Mother's Day (the 5yo spilled the beans

)
There are some really expensive items but don't let that scare you just keep clicking through and you can find some of the smaller pieces for a really reasonable price (considering it is a work of art that lasts forever). If you need guidance, give the ladies a call at the store - they are fabulous and can stear you in the right direction.
Good luck & let us know what you decide to do.
PS - they are on Facebook too if you want to see how people have them displayed:
Carruth Studio