It seems pretty healthy to me.
Does it get enough sunlight?

Maybe t much water, or water sitting on the plant to long

"soft and gooie" sounds like rot to me.
I'm thinking your mum's cactus is a goner.

What kind of potting mix is it in?
Can you get us a better picture with more light maybe? I can't see any color changes.

If it is soft, you should remove it from the mix and look to see if it still has any healthy roots left.

If it is soft and gooey, it is dead. If it is just soft, it may still be alive.

Check the roots, and always remember the golden rule when watering.."When in doubt, don't."

Christopher

Looks like the plastic pot sits inside a decorative pot that may not have drainage. When watered does the water runs right through the first pot and sit in the second? If so, it's a situation that should probably be avoided with any future c&s :)
It takes a lot of effort for some cacti to bloom and they may need an extra watering at that time. I echo what others have said: soft to touch, and you may need more water. Gooey (actual goop and juices) and the cactus is rotting.

-Ming

I think this is a cactus that changes color when it is stressed.

sorry for the delay in reply, (thought I set email notifications on)

I'll upload better image to orrow

it sits in a north facing window (they dint have south facing)
it is watered from the bottom
the soil mix is the one it came with (most likely peat based)
it is in a plastic pot 5.5cm three holes on base.
it also sits in decorative pot, but it is sat onto of a chunk of polystyrene to raise it to pot tip, (there is around a bout 1.5inches from the bass of decorative pot.

it also also worth noting the cactus is changing colour and going "gooie" where the blooms are and they have all dropped. the idea of it being stressed is a good idea, how do I make it happy if it is stressed?

thank you

leo

heres a close up

and thats the roots

at a closer look i think its been over watered?

Any areas that are "gooie" as you term it have rotted, and need to be removed ASAP if you want to save the plant. It would involved cutting until you see only green healthy tissue. Rot spreads quickly.

Christopher

Okay, as you can see it's the whole of the top (the colour difference) would it be safe to cut the top off? or shall I just buy her a new cactus?