It may reduce your stress to know that these family dynamics are more frequent than most people would believe!! As Vanilla suggests, you need to act. That might entail committing a few days to visit Ireland and engage a solicitor for yourself as (from personal experience) this is difficult from a distance. The Irish Law Society has a list of solicitors' firms here which can be searched by location. [broken link removed]
Meanwhile you can prepare as thoroughly as you can to keep costs down. Write out an account of the situation with - as far as possible - dates, contact details and brief details.
If you do not already have full details of the solicitor with whom your sister placed the probate work (processing your late mother's affairs, tracing and sorting accounts and paying dues etc., sale of assets) then you need to write to your sister formally asking for contact details.
It is difficult to keep going with such business when one is depressed and stressed after loss of a parent. Having a clear, brief written account of the situation and all the necessary information, dates and contact details and a clear, single "instruction" for the solicitor you appoint (you have to think exactly what it is you are requiring your sister to do, and why she must do it) will facilitate closure and the good outcome you desire.
I wish you well with it.