Passport required - or will a driving licence suffice?

My friend has received an invitation to her school reunion in Dublin. But it's in two weeks' time and her (Irish) passport has expired, leaving her no time to get a renewal.
She is of the opinion that she can take the ferry with her car and just present her (UK-issue) driving licence. It would be a great pity if she was turned away. I think she'll be ok with it as she lives in England and her car is also registered here. But she's in her 80s and has no internet, so I said I'd check with you lovely people on here.

I'll also double-check with the embassy on Monday, unless I get a definitive answer here, so no need to reply if that's what you would say.
Thanks in advance ...

No need for a passport, but picture (photo) ID is mandatory. It 'must be a photo licence and not just the paper one.
If she's got that, everything'll be fine.

Thanks, Lenny. :>)

http://www.citizensinformation.ie/en/moving_country/moving_abroad/freedom_of_movement_within_the_eu/common_travel_area_between_ireland_and_the_uk.html

but obvious check - make sure her driving licence is in date!

Even better! Thanks, Neverwinter.
xx

Assuming she lives in the UK, then UK and Ireland are a 'common travel area'.

http://www.citizensinformation.ie/en/moving_country/moving_abroad/freedom_of_movement_within_the_eu/common_travel_area_between_ireland_and_the_uk.html

That is the legal situation but some transport operators apply different rules - Ryanair won't let you on with a driving licence for example. So check what the specific transport operator you are using requires. Last time I took ferries between London and Dublin no one checked any identity documents.

iviehoff: The traveller is going by boat, so no passport is needed.
On the ferries only a driving licence is needed, nothing more.

Lenny, I have passed on the earlier answers so that's taken care of already - thanks.
iviehoff's information is useful for possible future flights - and could also be useful to anyone else with a similar query.
So thanks, iviehoff. :>)

The traveller is going by boat, so no passport is needed. On the ferries only a driving licence is needed, nothing more.

No passport is legally required when going by plane either, the fact that in practice one (or equivalent) may be required is due to the airline's own rules.

In the case of the ferries, they aren't very specific. For example, this is what Irish Ferries say.
http://www.irishferries.com/uk-en/faq/passports-identification/

And P&O are even vaguer. http://www.poferries.com/tourist/content/pages/template/routes_travel_information_kbyg_kbyg_checklist.htm

My experience is that in reality id documents are not inspected when travelling by ferry between Britain and Ireland, which is probably why the ferry companies aren't very clear about it.

Yep - correct, no passport is legally required when going by plane either, but you still won't get on board a Ryanair flight with just a driving licence (photocard or otherwise) as they don't accept it as ID.
Qhen I do UK-Ireland (both sides) I always carry a passport anyway, but have 'Never' been asked to show it.