As others have said, you can't know for sure, but you can look out for confirmation over time. Personally, I'm a big fan of love language theory, which is that everybody gives and receives love mainly through the five love languages-- physical touch, quality time, gift giving, words of affirmation, and acts of service. So, beyond doing what you ask of her or initiate with her, you might look out for signs like:
- initiating kisses, hugs, caresses, hand holding, massages, and other kinds of physical affection
- planning dates or trips together, going out of her way to be in the same room as you even if you're doing different activities, inviting you out for errands or to social events that are normally just her and her social group, or accompanying you to such errands or events
- giving you genuine, unique compliments, expressing appreciation for you, writing you love notes, sending you "I miss you" or "thinking of you" type texts, being forthcoming about what she likes about you, or thoughtfully written cards, poems, or songs
- remembering your favorite things and bringing them home when she encounters them, carefully selecting meaningful birthday and holiday gifts, or saving up for gifts for you that require her to go without spending on herself for significant time periods
- anticipating your physical wants or needs and meeting them ahead of time, taking on additional work to make your life easier or more comfortable, or actively looking for projects or tasks to take off your plate
Watch her for a while and see how much effort she puts into any of these things. She's more likely to do them, and do more of them, if she really loves you for you. They can be faked, but faked love language will seem less sincere, and it's hard to maintain for long periods of time.