I'm not sure why your mother needs to wait until 70 years old, if she have enough money before hitting 70 years old, why not? we don't know what will happen in the future, I recall back how the situation when Covid-19 happens, it's really hard to fly to other country, some country even forbid accepting tourists.
How much does Hajj cost from your country? $90 per month is about $1,000 annually, or $4,000 every 4 years
Seems like he only need around $3K per person, so it depends on how many person(s) will go to Hajj, 4 years is enough if the money isn't used for emergency needs.