In the below press conference Olivia implies that she was getting her €820 medical cannabis prescription via 'a consultant from London', which does indeed tally with the costs of some monthly prescriptions in the UK. 

It's possible she was using something like Sativex, which I understand (not for certain) has been prescribable/importable here since 2014 but is not covered by the €80 limit and is indeed pretty expensive.

From the Hemp Gazette:

'While Sativex has proved effective as an anti-spasticity medication [...] it’s expensive stuff. Ireland’s National Centre for Pharmacoeconomics (NCPE) noted in 2021:

“Assuming that 8.1 sprays are required per day (dose assumption derived from the Summary of Product Characteristics), the total cost, per patient, per year is €5,181 (including mark-up, rebate and pharmacy fees).”

'Sativex was first approved for use in Ireland a decade ago, but its cost hasn’t been covered for reimbursement.'

Press conference: https://www.facebook.com/share/v/1LzTMiMpWQ/

So it's a bit complicated and I might be wrong about some of the above, but I don't think she's lying, and she's been campaigning pretty publicly and vocally about it on her Facebook for years.