Can she just continue to ignore the motions indefinitely?
No - the Courts patience is limited.
My partner's solicitor has told him that the courts won't rule in default once solicitors are involved (they both have solicitors)
Actually, its just as well she has a solicitor - if she didn't there might be a view that she did not know what was going on. I think the Court will (ultimately) ask the Solicitor to explain why a default order should not be made. If client will not instruct the solicitor, they should apply to "come off record" - its a formal application and shows that solicitor has told client what will happen if they ( the client) do not deal with the situation.
People behave in marital breakup the way they behaved in marriage. Spouses should never be surprised at the others behaviour.
mf