I saw her comment on twitter where she implies she's never been told her accent was strong before, which makes me think it isn't, particularly.
People's perceptions of accent can be a bit bonkers. My DH went to a conference recently and chatting as he checked in, the staff commented they could tell he has come down from West Wales because of his 'strong Welsh accent'. I can't detect any Welsh in his accent; he's from a very english-speaking part of South Wales.
Obviously it's hard to judge your own accent but honestly if he sounds Welsh at all he's slightly less Welsh that Huw Edwards, the newsreader.
So from experience I don't even necessarily think she had a particularly strong accent for someone to say this.