Spend some time with her by yourself. Let her know she can always come talk to you and that your new girlfriend cares for her a lot and thinks highly of her. Let them spend some time together also. Knowing is a rational operation. Loving is an emotional one.
Some people call it love if their feelings are very strong and they are very attracted to another.
Some call it love if they have a great deal of respect for another. Some people say you will know it when you have it. Let's not get too hung up on the definition of love. Let's just say that if a relationship is very good and very strong, then it will both feel good and make sense. Your question makes sense rationally.