My mother-in-law is selfish and annoying

I just cannot get over the fact that she has never made my husband a priority, for years favoured her ex-husband who was cheating on her ... much to the detriment of my then-teenage husband, whom she neglected. Her ex-husband walked away with all her money. She never gave my husband money because “there are other children”. Yet, whenever she needs help she comes rushing to us and she’s not even in touch with the other children! She will ask for help clearing out her shop (removing carpet etc.) and she even asked me to do her a will (I am a lawyer). Yet whenever we need something simple, like a lift somewhere, she bails on is cause “she’s made other plans now” even though she agreed to give us a lift two weeks ago. I don’t have a mum so I relied a lot on her at the time of my wedding and she proved a let down- to had to pick my wedding dress in one day because she wasn’t prepared to come to more appointments with me, she was going to arrange a hairstylist which she never did leaving me with limited options at short notice. She also booked a trip abroad and didn’t return until late the night before the wedding. Her fridge was empty so I had to provide dinner and breakfast! She took the wrong shirt to be tailored for my husband to wear, and then suggested her ex-husband wear the very expensive shirt I bought my husband for the wedding day. Everything she touched, she fucked up. She also promised to arrange a hen night that never happened. I never had any time to take care of these issues myself as I was working a lot at the time. I also don’t have. mum. Later on, I invited my mother in law and my husband to my legal graduation and she never showed up as she “was in poor health and couldn’t be bothered”. Yet she never cancels on her friends. When I refused to write her a will, she took a huff until I did. I have been finding it increasingly difficult to tolerate her company and don’t really stay in touch with her anymore unless she messages first. My husband knows we have grown apart and suggested I should go out for dinner with her. I made a reservation and put down a deposit. It was fine to go ahead, but two days prior she cancelled on me because “she has to look after her dog” and I lost the deposit. She would never cancel on her friends. Yesterday she was contacting my husband to ask if I’ve fallen out with her “as I don’t message or call her anymore”. He knows the truth, but he said to her I’m just busy. I’m too polite to confront her and at the end of the day she’s still my husband’s mother. I also don’t think she’s the best role model for my future kids having a past of alcoholism and ongoing poor decision making in her life. My husband thinks she is “simple” as in not very intelligent. Any advice? How would you tackle this? Am I being unreasonable as I can’t even be bothered speaking to her when she calls? I just don’t feel like making someone a priority who doesn’t return the same treatment. Thanks x