May I play devils advocate and suggest an alternative interpretation?
She is downsizing to smaller house which should be on same terms then about 100k surplus to each of them.
This sounds quite reasonable, assuming that they owned the house jointly (probably as tenants in common as you seem to imply that the house would be left to his children in his will). The solicitor will know that that money from the sale of the house cannot be transferred to her, the surplus must be shared according to the ownership.
Many spouses find that they are landed with a property which is too large for their finances to run once the spouse moves into a care home and it is often the case that they then downsize, so that they can then live in a smaller, cheaper to run property once they only have their own income to pay for it all.
When a house is owned as tenets in common, this means that each individual owner can leave
their share of the property to whoever they wish - usually the children and this is frequently used when there are children from a first marriage. Please note, that it is only his share of the property that is inherited, not the whole lot as his wifes share of the property belonged to her before his death and will continue to belong to her afterwards. This means that when the more expensive property is sold and the wife downsizes, her portion of the surplus funds has always belonged to her. She cannot sell the property to release funds for herself that would otherwise go to to the children (so long as the solicitor has done his job properly and I have no reason to doubt this). I also doubt that she is keeping his share on the funds as you said that he will now become self -funded - so the fees will have to be paid from somewhere.
The money that you would lose from inheritance is
his money which, while he alive should be used for his care.