It should not be a problem.
To explain a bit more: the valid PR card is evidence of PR status but it is separate and distinct from the PR status. PR status does not 'expire.'
If she has been in Canada two years continuously, she is in compliance with her residency obligation. I don't think that's relevant to your application described above, but certainly there's no danger in showing the expired PR card to IRCC. (If they think it's relevant, they'll look up in their own files).
Where the residency obligation (being compliant with) definitely is relevant is for a sponsorship application - i.e. if you want to have her sponsor you for PR application. Even for a sponsorship application, the PR card itself is not relevant, being compliant with (and resident in Canada) is relevant. In other words, she can sponsor you if she is compliant with the residency obligation at any time, regardless of whether she has a 'valid' PR card.
I don't know your situation but in most cases, it would make sense for you to apply for PR status (have her sponsor you) at some point.
(There is one small advantage to her applying for the PR card soon, which is that once she demonstrates she is compliant under a new PR card application, there probably won't be a new examination of her compliance for sponsorship purposes. Probably not a big difference but could save some time.)