Hello @StrongCoffee - Had I called an ambulance last night they would have kept me in for monitoring. As my blood pressure was OK I was not overly concerned, hence not calling the ambulance.
If you are concerned it is a good idea to stay with your Mum overnight after she has the vaccination, just for peace of mind. If her GP or specialist was worried about her and possible reactions they would have set something up but it is not done as part of the vaccine program. She may have no problem at all.
The chills are a basic reaction as are headaches and feeling tired. Nothing to worry about.