It's wonderful that you're so conscious and aware of what your granddaughter is digesting! As a parent, grandparent, or child care provider, it's really up to you what you feel is appropriate for the maturity level of the child in question. In my opinion, I would say that a small amount of love or romance is okay for a fifth grader. Many of the most popular children's authors for that age group do add in some school crushes, in order to keep things relevant to kids (crushes are a big part of that age level).
If you're looking to find books that are specifically targeted to fifth graders, you may find our grade-specific reading lists helpful. Below, I'm including a link to this year's fifth grade list.
We've been dealing with this issue with our fifth grader as well! In the spirit of full disclosure, I will say that I am an ultra-conservative parent. The mantra in our home is that you have 18 years to be a kid and 40+ to be an adult. So, with that said...
We tend to be more conservative in the books that we let our 5th grade son read. The road adulthood is definitely a one way street, no need to put her in the fast lane with love and romance! We try to encourage books on friendship that focus on good character traits like loyalty, integrity and modesty. I recently bought him a few of the books that I read in 5th grade like Old Yellar, Island of the Blue Dolphins, A Wrinkle in Time, and Black Pearl.
My friends with girls recommend these books that may be worth mentioning to her:
The Canning Season (P. Horvath)
The Lady Grace Mystery Series
The Sisters Grimm Series
The Secret Garden
Because of Winn Dixie
Thora (which is about a 10 year old girl)
There are tons of books that she'll be sure to love depending on her hobbies and interests. I admire your support and encouragement! Grandparents have a HUGE impact of kids these days! Way to go!!!
Your granddaughter is in fifth grade? Well it depends on the level of romance or love in the book. If it's something that she hasn't learned about yet in health class, then no she should not read the book. If she is educated about sexual things through non-educational books, then she could get the wrong impression about it and think it's okay to do those things.
You or her parents could read the book first, then deem if it's appropriate or not. You could also talk to the school or public librarian and see what they think. You should be comfortable with the books your granddaughter is reading. I hope this helps!