She is very vulnerable and delaying a scan for a few weeks might be preferable to catching a very aggressive virus, of course the hospital will be prepared to protect patients but there will also be patients with the virus in the hospital so on balance it may be more sensible to wait a few weeks until the risk of catching Coronavirus is considerably less
I've read some appalling advice on this site but, at the time of writing, yours is absolutely up there as the worst of the worst, softygirl.
Do you have inside knowledge as to how this virus will progress? If you're only as informed as the rest of us how can you be so confident that the risk of catching it will be "considerably less" in a few weeks' time?
Perhaps you haven't read Professor Charles Swanton, Cancer Research UK’s chief clinician, statement that some cancers will become 'inoperable', rather than survivable, if diagnosis or treatment are delayed by the pandemic?
Please, OP, take no notice of this misguided poster and encourage your dm to keep her appointment. Her life could be at far worse risk if she fails to attend and if her case was considered to be non-urgent the hospital would have deferred her appointment.
Also, please be reassured that exceedingly stringent measures have been put in place to ensure that no cancer patient will be unduly put at risk while undergoing diagnosis/treatment and, to make doubly sure, your dm should wear a mask when travelling to and from the hospital and use a hand sanitiser frequently during the journey.
It's entirely understandable that you don't want to "make the wrong call", but you'll never forgive yourself if you encourage your dm to not attend this appointment only to discover at a later date that her chances of recovery have been significantly impaired, or worse. because she wasn't scanned and therefore her treatment wasn't started earlier.
I hope that you, or a trusted friend/relative, will be able to accompany your dm and no doubt her results and susbequent treatment will be provided in a location nearer to her home.
I also hope that you'll come back on Friday with an account of your dm's experience which will encourage others to not even think of delaying essential medical investigations and/or treatment during these trying times.