There can be a fine line between unbridled enthusiasm about a person, especially a new friend or relationship, and what others would see as stalking or harassment. The "honeymoon period" in new romantic relationships is known for intensity and it is common during this period for two people to want to spend all of their time together. The important difference between a honeymoon period and stalking is that in a honeymoon period, BOTH people really, really want to see each other.
Some questions to help figure out stalking vs. new reciprocal relationship
1. Do both parties contact each other and invite each other for activities?
2. Who initiates contact?
3. How long have they known each other?
4. Is it a socially appropriate relationship? Is there an unacceptable age difference? Is there potential for the person on the spectrum to be taken advantage of?
5. Are they giving gifts that seem to be "too big, too soon"?
Your daughter may not understand the unwritten social expectations of making a new friend (especially if she's sexually attracted to him). There is a relationship progression that is typically followed: acquaintances may become friends, those friends may become really good friends or best friends, and sometimes those relationships become intimate, romantic relationships. With online dating, a few steps might be skipped but there is still an expectation of a type of progression: getting to know someone, seeing if there's "chemistry, and meeting in person several times before becoming an exclusive relationship.
We find that often our loved ones get taken advantage of by others who are attracted to their great desire to connect and have relationships but who aren't as socially savvy to spot if they're being played. Our role is to help with perspective taking and to make observations to point out those hidden, elusive social rules.
It can be hard to accept rejection and it can be even harder to accept and recognize subtle rejection. I frequently see difficulty understanding the "Minnesota No;" if someone doesn't reply to any of your communications that's a good sign that they don't want to communicate with you. Here in Minnesota we also tend to tell people that their behavior is "okay" when we don't want to hurt their feelings. Our literal thinkers then hear that they're not doing anything wrong because they person told them so when, in fact, the other person is at that moment filing a restraining order. Explaining the communication style here in Minnesota is crucial for helping your daughter understand that she might actually be experiencing a passive rejection.
What to do?
Reiterate to your daughter that her safety and happiness is your goal. If she is stalking, she could get in trouble with the police and even end up with a criminal history which could impact her ability to volunteer places and getting hired.