I have lived in Maastricht. Everybody speaks Mestreechs, fluently Dutch and English.

Be reminded that taxis are usually provided on call. Better to let your hotel reserve one. Some are bigger to handle mobility impaired passengers. If the driver is friendly, ask him to pick you up after the show ends - usually the whole crowd exits at the same time and it can be maddening waiting for a taxi to come available ... Better have one pre-reserved so your mum doesn't need to wait standing.

If you need tasty restaurants, try out the tongerense straat - the most cozy terras square of "Onze Lieve Vrouwe plein", the old water mill and traditional vlaaierie (limburg pies) "bisschopsmolen", very good icecream of "luna rossa" and if you like to treat her to fine dining with a view or in a limestone cave try "chateau neercanne"


Enjoy!