Wet rot on interior window frame

[EmbarrassingHadrosaurus]

My MIL has a bit of wet rot in a corner of an interior window frame (condensation problem and her house has aluminium windows with a wooden framing).

I'm a little unclear on how to fix this for her. Do we dry it out with a fungicide treatment and apply a wood hardener? Or is there a different method/sequence of treatments.

Any product recommendations, please?

It's a hardwood frame so it wouldn't be easy to remove the timber and replace such a small section.

Hi @EmbarrassingHadrosaurus it's difficult to say without seeing it but if it's a small area I'd dig the rotten wood out and add rot hardener to the exposed underneath wood. Then fill with weather proof wood filler. The other option is cutting a rectangular area out, add hardener then glue a slightly larger piece of hardwood into the area (which will need sanding /planing to size) . Have you got any woodworking/carpenter friends you can consult?

Thank you. Unfortunately, I don't have anybody to consult and we're generally having no luck persuading any local carpenters to come and have a look.

I've uploaded a photograph as I'm unsure as to whether it's wet or dry rot and if it would make much difference to the treatment. It's the interior corner of a window in a room that has condensation. The hardwood trim is spongy and dry for about 8cm and now seems to be collapsing. I'd like to treat it before it spreads to the windowsill or starts to grow vertically.

MiL doesn't want me to use woodfiller because she likes the wood. However, I wonder if she'll have to reconcile herself to woodfiller and some paint after it's treated.

Looking at the photos I think you need to cut/chisel a section out and replace with a piece of hardwood the same size. It also looks like the timber all needs treating, with oil or varnish. Condensation has likely caused the rot. To prevent it reoccurring the timber needs to be sealed.
Have you looked on YouTube? There's likely to be someone repairing rotten wood (there's a YouTube vid for almost every occasion). It could help you with the task. It's hard to explain in words.
Good luck with it. I'm sure you are capable of the repair but guidance will undoubtedly help a lot

@EmbarrassingHadrosaurus on reflection it might be easier to remove the whole length and replace. It may be pinned in place and fairly easy to pry off

Thank you for that advice. You were spot on, it was easier to remove the whole length and the fungus had spread further along than was visible from the top.

I've now applied treatment and hardener.

Good work @EmbarrassingHadrosaurus. Whatever you replace it with make sure to treat and seal it and do the same with the existing timber