This may be part legal matter, part just finding the best way to make things clear:
Having a surveyor come out and stake the corners again may help her understand. You might try the surveyor who handled the subdivision for the builder, but you may find surveyors at less cost by calling around.
Yes, a letter from an attorney, with a copy of the survey, and some indication of a willingness to help spot the corners might help. This could be done in a tone that would suggest friendliness in maintaining the relationship as neighbors.
If there is an association, management agent or the ability to contact the builder, one of them may be able to write a friendly, but firm letter to assist.
Otherwise, if you feel the situation warrants it, you can try to involve the police regarding trespassing, but my expectation is that they will tell you to handle it as a civil matter. Perhaps there is some chance, with your survey in hand, they may at least speak with her about respecting the property lines.
Otherwise, you may have to file suit.
Before taking any action, you should review the situation more carefully in an office consultation.
Mr. Repay has covered the bases, I might add that sometimes with aggressive neighbors there is really no remedy, they seem to have sort of compulsion and can only be contained, not stopped.