OK, she should probably just make a tax return now and point out that she is declaring all her dividends in one year. I would guess that Revenue won't get too excited about it.
But sell the shares if she is worried about stuff like this.
The advantage, though, of holding onto shares until she dies, is that capital gains disappear on death.
She probably has a CGT bill if she sells them now.
But freedom from worry is more important than maximising the tax efficiency.
Brendan