Hi there...
I read alot of messages on this board when looking for my bike.
In you will see a barrage of negative reaction from people about buying department store bikes, etc.
Things to keep in mind:
1. Budget, if you only want to spend less than $100...then stick to your budget. A lot of people on this board probably ride bikes $1000 or more...
2. While the quality and service may not be the same as a "brand name" bike from a LBS, if she's riding 3 times / month, it's a BIG difference from a lot of the enthusiasts here that ride 6 days a week, 10+ miles each time. If it's very low usage, then most bikes will probably be OK. Don't jump off and cliffs with it...but riding down the paved street is alright...
3. Think about getting a used bike. Its a good compromise, you'll get quality bike that will last (in case she gets really into biking) and can stay within your budget.