Honestly, it's going to come down to words+actions. Does she say she's in love with you? Does she act like she's in love with you? If you don't think she is, but feel like she should be, it might be a good idea to sit down and talk with her about your uncertainty and how you feel.
This is hard to answer because people express their love differently. Love is generally shown in the smallest of ways. I would look for the little things that she does for you that maybe go unnoticed by you.
The best thing anyone can do to get that kind of answer is resumed in a word : communication.
And I should add also : trust.
Nobody can know exactly what's happening in someone else's mind, and how that person feel "love".
What does it mean for you, to "really love" ? Does it mean you want her to be able to die for you ? Or to be there even when you fight, are old, hurt, or when things are not glamorous, like for instance when you're so sick you need help holding your hair when you're throwing up and taking care of you when you're crawling up on the floor shitting yourself ? Because hey, if that's not love, what is ? ^^
And trust, because well, even when people are "really in love", we never know "for sure", not even them, by the way : life can happen. Feelings can fade away, or feelings for someone else can rise and grow... In the end, it's a combination of trust and communication, and getting in touch with your mutual needs and boundaries.
So my tip here :
- find what you need / want in a relationship at the moment (no string attached ? polyamorous or monogamous ? live together ? meeting parents ? just enjoying the relationship without thinking about the future ? etc)
- talk with your partner to know if they share the same common view about love and relationship
- find out if your views are compatible in this relationship and if you're ok with her own conception of love relationship.. and share yours with her :)
The trust part is something to work on on your own though. It can take some time, but eventually it's worth it :)
Love, for me, isn't when one needs one another. But when one WANTS to be with one another, even if they don't need to. ^^