sentences like " ona li tawa e tomo " usually "means he moves house".
To say "he moves himself to the house" we say "ona li tawa tomo".
Similar logic could be applied (i suppose) to "ona li monsuta e soweli".
For me it sounds more like "She got him scared" than "She afraid of him"
May be some form like next could make it better.
ona li pilin e monsuta (tawa/tan) soweli.
ona li jo e monsuta (tawa/tan) soweli.
actually it is pretty common use of "pilin monsuta" to say "afraid" and "li monsuta e" to say "to scare".
https://tatoeba.org/eng/sentences/searc ... und&to=eng