Why has she started weeing in her bed

Staffy lover wrote:Pixee is approx 16 to 17 months now, she was found a stray, so no one knows her real age. She goes on a walk in the morning for 45 mins to over a hour. Then later have a play in the garden. In the afternoon she has over a hour walk. Sometimes last thing at night she has 15 mins walk. Often she will get 2 hours walk on a night, if time is ok. She is always put outside last thing before we go to bed. Her routine is, when we say come on bed bye times, she goes to the back door to wait to be let out, as she knows she wont be allowed to bed otherwise. I dont think she drinks a lot, we have a big bowl of water, she will drink about 1/4 of it at least through out the day. I have never had a problem taking her out in the middle of the night. Its just she didnt wake me up. And unforuntaly she did it again this morning at 5am. Hubby heard her moving about, but didnt think to wake me up!!!!! She has always woke us up by putting her front paws on my side of the bed, as this will wake me up, or walk round to hubbys side. Dont understand why she hasnt. We generally take her, well me, for a wee in the night, then if she keeps waking us up every half hour later, we know its not the toilet she needs but just pushing her luck wanting to get on our bed. She is allowed on when the alarm goes off, for a cuddle then she goes back to sleep lol on our bed. I wouldnt say she is anxious now, as she is settled.