If you have a hobless (brick surround) shower which is at the same level as the rest of your floor (a small 1-3cm lip is fine) and the shower is not a pre-fabricated plastic/fibreglass base, then yes, theoretically you can install floor heating into your shower area.
When considering putting floor heating into your shower area, you should consider whether there are any complexities such as strip drain position, glass shower screen fixings, which are positioned such that the floor heating could accidentally be damaged when they are being installed. We advise that if your shower will have either of these, ensure you stay well clear of these areas when installing your floor heating.
Another consideration is whether you need it in the shower. If you only have a small shower area which when the water is flowing gets covered in water, then as your water will be hot, there is very little benefit putting floor heating in. If you have a large walk in shower and the water is only at one end of it, then yes it may be worth continuing your floor heating into the shower area so that you don't have a cold area.