Since you've never met her mother, and have only met her in person one time, something to think about..... She may be the one who wants to call it quits and is using her mother as the excuse. A "gentle" way to do it is to put the blame on someone else.
On another note, if I were her mother, I'd probably be equally as concerned because of all the horror stories that have resulted from Internet dating. This isn't being said with any disrespect to you personally, as I don't know you. I'd be doing everything I could to discourage a daughter of mine from following this path.
As a Christian, if she were my daughter I'd be very disappointed in her for inviting you to her home for a weekend. Regardless of what did/didn't happen between the two of you, the implication of sin is there now and won't be easily erased.
If you were my son, I'd be looking at this from a different viewpoint. First, as a Christian, I'd be disappointed in you, as noted above. Next, I'd be telling you that you don't want to become further involved with a duo of both mother and daughter. If the mother is as controlling as you say, that won't end. You have to factor that in for the rest of her (mother's) life. Are you ready to deal with that for 30 or 40 years? Suppose circumstances force mother to move in with daughter. It happens, often, when elderly parents can no longer care for themselves.
Are you attending church regularly? If so, talk to your pastor. An online forum, no matter how concerned we are for you, comes in a distant second to talking to your pastor face to face. To ask your pastor to pray with/for you for the Holy Spirit to guide you.
If you don't attend church, please find one.