Was this the right thing to do? Am I in legal right? Do I have to pay a gift tax or inheritance tax come tax season?

I'm 25 yrs old and my father recently died from cancer 6 months ago. As far as I know he did not have time to make a will before he died. Once he died my mother (who has been jobless since I was 7, does not have a license, and is a hypercondriac) asked me if she could put some money she got from my father dying in one of my accounts because she was broke and wanted to be able to get food stamps and heap to help with the bills until she got a job and having that money in her account would not let her do so. I let her because I trusted her and was so wrapped up in my fathers death that I wasn't thinking. I didn't know how much the amount was and didn't know she took the check book and debit card for the account. Then I started seeing her buy new clothes all the time and a new $3000/5000 shed (unnecessary things) and was curious as to how much she put in my account. I looked and it was close to $200.000. And found out she had writeen 3 checks forging my signature. One to an insurance company, one for his tombstone and one to her own account. Nothing for house bills or mortgage or the clothes or the shed. She had to of been paying the bills some how for the past 6 months. Then I started snooping to see if she had any other money comming in. As now she's on food stamps and heap and still hasn't goteen off her ass to get or look for a job. Oh yeah, and she charges me rent to be there. I found out she is getting money comming in from both my fathers retirements every month for the rest of her life, and his $93,000 401k comming in a month or two. Plus she has around $7,000 in her own account and a couple thousand stashed in her room. And I checked on the mortgage as it is a matter of public record and it says the house is payed off, yet she says they refinanced and still owes $160,000 on mortgage. My mother is not someone who is easy to talk too, makes everything an arguement and lies about everything, I do not know what to believe or what to do in this situation. She has forged my signature on checks, has not tried to get a job, is taking advantage of the government to get food stamps and heap, has all this money (that I'm pretty sure I'm going to have to pay some sort of taxes on come tax season) in my account and hasn't given me or my 20yr old sister a dime. And besides all that there is other personal problems me and my sister have with my mother that is too much and too personal to get into in this blog. My sister up and moved to Florida with her boyfriend, where she is struggling to make ends meet with bills and working too job and I just moved the money in my account to a different one where she has no access to it and moved into an apartment in the middle of the night without her knowing and left her a letter explaining why. The next day I get the voivemails from her saying she's going to kill herself, that she has nothing to live, she's going to kill herself..which guilt tripped me into calling her back to make sure she was ok as I do not want her suicide on my conscience. And there she went, lying about everything and telling me I must give the money back, she is broke and has nothing and she cannot believe I 'stole' from her, or it will become a legal matter. What legal matter can it become? She completely signed this money over to me, has been forging my signature in checks, making me an acessory to fraud and doing so so she can take advantage of the government and not get a job. Not to mention not give me and my sister a dime. I plan on using the money to set up mine and my sisters future. Helping us both go back to school, with bills, incase of emergencys and to help keep us away from all this emotional heartbreak and drama. Yet with my mother and everyone who believes her sob story calling me and harassing me and telling me I'm a horrible person for what I've done to my poor mother, I'm feeling more guilty and emotionally unstable. I need to know if I've done the right thing, was I in legal right to keep the money that was signed over to me and how much and what kind of taxes am I going to be stuck paying since this money has been in my name this year. Someone please help.