If she is weeing outside her tray, or inside it but aiming wrongly, the problem could be due to one of two things.
Either the tray is not clean enough by HER standards, not yours. If this is the case give her two clean trays and see if it helps.
She is old, so does she have rheumatism that makes getting in and out of the tray difficult?
If so a tray with lower sides might be the answer.
Have you had her checked by the vet? Female cats are practically as prone to chills on the bladder as we women are.
And elderly cats (and dogs) can become incontinent.
Is she distressed by this habit of weeing all over the place.'? If she is, then there is a physical cause most likely. If she isn't, she is either cross with you because the tray is not clean enough by her standards, or she is doing it deliberatly to provoke you, being in a huff about something else, or she is suffering from a form of senile dementia.
I realise going to the vet is expensive, but if there is a physical cause it needs either to be treated, or you and the vet need to agree that the end is in sight and let her go now.
Hard yes, but letting the cat go downhill slowly is worse.