iOS Mail - default account issue

[BG24BR]

My mam (who is 93YO and in a care home) uses an iPad extensively to keep in touch with family. She's been using a UK v****n.n*t email account for free seemingly for ever. I've been expecting it to be closed down for at least the past 10 years but it's still sending and receiving OK .. BUT just in case, I've set her up with a gmail account. The issue is that whatever I do, I can't get the iPad to set the gmail account as the default one for sending messages. Yes, I've altered the default in Mail settings. Yes, I've re-started. Done all these things seemingly a squillion times. The system shows the gmail account ticked as the default, but whenever she sets up a new message to send it ALWAYS shows that it will go from the v****n account. I don't want to close the v****n account as she does use this a lot and until the gmail account is set up - and working - as default it would leave her without one. I KNOW that she could tap on the account name in the from: line, and change the sending account, but try getting a 93YO to remember how to do that?? I KNOW she could change to use the gmail app, but a 93YO who has used the same app since her first iPad in 2010 isn't likely to adapt so easily. All suggestions gratefully received.