Two separate but linked procedures are in play here:
The PCN
Let's say she didn't receive any of the statutory notices (until we know more we cannot be precise about which e.g. was it a parking, moving traffic, bus lane contravention etc...). Whichever applies, the last notice would have been an Order for Recovery. Having missed this, then as regards the PCN she(presuming she was the registered keeper) would have to make an Out of Time submission to the Traffic Enforcement Centre, as per Incandescent's post. Likelihood of success very low.
The bailiff
The bailiff's fees dwarf the council's penalty ( probably £310 to bailiff v £205 to council) so if she could avoid a significant part of the £310 she would literally be quids in on the deal.
Ask the bailiff when the Notice of Enforcement was sent and to what address and post the notices as per previous post.