My mom have been paying to Unicef $12 a month for years. I told her about ideas behid EA. If this is an easy task she would be willing to switch her payments to any of EA charities. She has her bank account in Poland. Is there an easy way for her to donate?
https://www.effektiv-spenden.org/ offers SEPA, but there's no English site yet.
Are card payments not possible for your mom? There shouldn't be a problem to pay to GiveWell or for that matter to most of the charities in EA from within Poland. Check here: https://secure.givewell.org/
Or is that not an option and it has to be a bank transfer?