I cant catch my mare?

i got my 2 yr old mare on monday, shes lived out her whole life and only come in to have injections done, never had feed, carrots etc, we put her straight into the field, went to catch her tuesday and she ran off straight away, did some join up and she kept us just out of arms reach. so the owner of the yard got her in for us, shes been in the stable for 3 days, we let her out last night because she was showing great improvement, she was doing join up great and following me round, eating out of the bucket and out of your hand, so we though shed be ok to go back in last night, she walked off and she let me catch her and stroke her and give her a treat. we went back today and as soon as she saw us she ran off, we did more join up and she kept her ear on us, licked and chewed, lowered her head and didn't want to go far from us, but wen we actually got close to her she would just run off again, shes got a bit of rope on her headcollar to grab onto, but she keeps us just out f arms way to get to her before she runs off again, wont even let us stroke her or give her a treat. we tried the fee bucket but the other mares just chased her away so we gave up with that, anyone got any advice?