How does Anne describe love?

It is difficult to know exactly where in the book you are referring to. Anne mentions love in relation to her fondness of her father and her strained relationship with her mother. She also mentions love in relation to her new crush Peter. You can see here expressing a very addolescent view of romantic love,

In the meantime, things are getting more and more wonderful here. I think, Kitty, that true love may be developing in the Annex. All those jokes about marrying Peter if we stayed here long enough weren’t so silly after all. Not that I’m thinking of marrying him, mind you. I don’t even know what he’ll be like when he grows up. Or if we’ll even love each other enough to get married.

As Anne matures, so do her ideas of love,

Love, what is love? I don't think you can really put it into words. Love is understanding someone, caring for him, sharing his joys and sorrows. This eventually includes physical love. You've shared something, given something away and received something in return, whether or not you're married, whether or not you have a baby. Losing your virtue doesn't matter, as long as you know that for as long as you live you'll have someone at your side who understands you, and who doesn't have to be shared with anyone else!