These are tough as old boots. You can prune them however you like. But do it just after flowering to ensure bloom next year.

She loves the blooms but reluctantly agreed to a gentle pruning. I'm thinking I'll just reduce the long branches. Thoughts?

==>>

absolutely NOT ..

google rejuvenation pruning.. and prune properly at about 3 inches... 1/3 of the plant should be pruned out every other year or so ..

https://duckduckgo.com/?q=rejuvenation+pruning+of+flowering+shrubs&t=ffab&iax=videos&ia=videos

watch some of the videos there....

NEVER prune this type of shrub at height.. or you will have structural problems in a few years.. it will start flopping due to the weight at height..

timing for any pruning of this type is always after flowering ...

if you cant convince her that doing it properly is better.. than doing it gently.. then just back out now.. or else she will be blaming you in a few years .... gentle??.. schmentle.. lol .. as flora inferred/implied.. this is a 'run it over with the truck' bush.. not some foo foo special baby that needs tlc... now go do the right thing.. full throttle.. lol...

ken

I agree with floral that this shrub can be pruned as hard as you like, whenever you like (being mindful of flowering times) and as often as you like. Don't worry about rejuvenation pruning techniques - they don't really apply in this situation. And I don't even understand the comment about never pruning at height...wtf does that mean? btw, never say "never" when gardening - it simply does not apply!

The most handsome planting of flowering quince I have seen were several trained up against a retaining wall as espaliers. Those required rather extensive and consistent pruning but they flowered heavily every spring.

Chaenomeles are often grown as espaliers against walls here, just like apples or pears, to which they are closely related. There is no need at all to do rejuvenation pruning if you don't want to. This is not a caning shrub. They can be cut back wherever and whenever you like.