Aggressive 2 months old weimaraner puppy!?

OK i have a 2 month old weimaraner, she we believe she is a purebred but are unsure.. we found her at about 5 or 6 weeks ... i took her to the vet and she was malnourished covered in flees and wormy.. she is quite healthy now but is showing very concerning behavior... she is very smart and is starting to respond to sit commands.. i am a stay at home mom with a young son so i can stay pretty on top of her training... the thing is she is getting more and more aggressive , biting , nipping ,screaming and ferociously biting when gently held on her back ... i have researched all types of different sites and used a combination of techniques .. like i said she is doing really well at the sit command ,, stay is next... when i give her the food i make her sit first ... then when I give it too her i put my hand in front of the bowl and make her wait a min then she can eat.... when she is done back to her crate for 10 min and then outside .... she goes in the same spot each time... then its back inside and i keep her right next ti me and rub her , or cuddle... she likes to paw me then nip... when I saw no she growls and when put on her back she screams and shows her teeth lips pulled back and snarls... she has bit a few times... when she was sitting next to me to day she jumped up and bit my throat and chin... i said NO and flicked her nose not hard but enough to stun her.... she then started to bite my hands and i did the same thing... then i put her on her back and tried to gently rub her tummy and chest then she started snarling and screaming ... i looked her straight in the eye and over and over in a very deep , calm tone said your not the boss...until she calmed down a bit she ended up falling asleep , but as soon as i moved back to snarling again.... i am very worried that she wont grow out of it and i have 2 young children 1 is a toddler.... i don't want to give up but i don't know what else to do... we live in a small town so there are no obedience schools anywhere near.....ughhhhh help ....