Given the situation you describe - you don't seem to have the information to connect the profile of this person, I infer you probably have minimal reliable/accurate detail about the person to base a profile on (birth date and place). you describe them as a 'distant' relation (in fairness a first cousin once removed is not particularly distant, unless you mean geographically, but I digress) which says you probably don't know if they might actually be interested in joining Wikitree, how they might feel about having their information online, etc. (have you ever met or spoken on the telephone with the person?) Moreover the specific person you are considering inviting is related to you by marriage not blood.
If the person decides not to accept your invitation there is (if my assumptions above are correct) now a privacy protected, orphan (i.e. unconnected) profile, with (estimated?) dates and places.
Given all this I would probably just send her an e-mail privately and ask her if she is interested in joining and if so would she like to help get her started on Wikitree.