Your guilt may stem from the fact that you are putting Lori in situations where she is forced to order the cheapest thing on the menu. You are not obligated in any way to pay for Lori, but as her friend, you are obliged to show empathy and support for her financial situation at this time. Stop setting up test situations where Lori is doomed to fail. As far as gifts, don't spend beyond what you feel comfortable spending. If you buy her expensive presents, and she doesn't have the means to reciprocate, you are setting yourself up to feel resentful and angry.
Friendship needs a level of equality.
Buy her less expensive presents that won't make her feel uncomfortable or indebted to you, or embarrassed about what she can buy you. You may also want to make friends with those who have the money to go to the places you enjoy. That way, you won't feel deprived and won't resent having to go to less expensive places with Lori. Look within yourself to try to understand why Lori's economic situation annoys and upsets you so much. Acknowledge that perhaps you enjoy showing off your money, and at the same time you feel guilty about it.