IMO, if she's more interested in what you can do (ie usefulness) for her than knowing you as a person. Those who are actually serious about getting into a relationship with another would be more curious as to your personal tastes (eg food), hobbies or even views on political subjects. In other words, they make an earnest attempt at engaging you at a much deeper level, even if it could potentially lead to unpleasant conversations. After all, if this is their potential life partner that they are talking about, they would want to make sure that it is someone that they can put up with in the long term.
For example, one of the first questions my wife (she is a local, not a foreigner) asked when we started dating was whether I was a smoker. At that time I was. But she liked me enough to put up with it and I tried to avoid smoking on your dates. But she always made it a point to nag at me that "You really ought to quit smoking if you want me to be more happy with you". I did quit in time after our marriage.
Besides that, "visa chasers" tend to quickly drop the act the moment there's some form of delay in getting their visas. For example, they sweet talk you everyday while persistently asking for an update on the visa. And if there are snags, they are quick to show their temper. Another potential red flag is if they ask you to lie about certain things when filling up the form. Someone who is genuinely interested in you won't want to risk getting you in such trouble.