There are three types of ESA:
Someone living in an area where Universal Credit has been introduced (or who is already receiving Universal Credit or who has received it within the past 6 months) is entitled to claim 'New Style' ESA but only for up to a year. 'New Style' ESA is NOT means-tested.
A person who doesn't fit into the above category, but who has a recent full record of National Insurance contributions, is entitled to claim 'Contributory' ESA but, again, only for up to a year. 'Contributory' ESA is also NOT means-tested.
A person who doesn't fall into either of the above categories (either because they never qualified in the first place or because the 1 year limit on the above types of ESA has now expired) might be eligible to receive 'Income-Related' ESA. However that type of ESA IS means tested and anyone with savings of over £16,000 won't qualify.
So, if your friend has been on ESA for over a year (or otherwise doesn't qualify for the first two types of ESA above) she is now no longer eligible to receive it.