If the conviction was over 10 years ago including conclusion of any probation, fines paid etc. and no further convictions since that she may be deemed rehabilitated provided the conviction was not for something that could result in at least 10 years imprisonment. If the conviction was outside Canada there must be a charge under an act of parliament in Canada that would equate with what she was convicted of for her to be found inadmissible so it depends on a number of things. Further details would be required.
She was convicted in the US of several misdemeanors in the 1990s. There is nothing outstanding. Can she have her fingerprints done at the RCMP or will that be a problem as she is here illegally?