Trying to teach my dog being alone is okay

Recently I rescued a dog (about 3 weeks ago). Her previous owner had 6 other dogs and couldn't take care of her anymore. She has no training and isn't house trained either, so we keep her in a pen with puppy pads at night while we try and potty train her. We've found that she hates being separated and confined in any way and always tries to escape. I've tried a few methods like giving her toys with treats, feeding her, slowly acclimating her to being alone but she still cries and howls through the night. I'm not really sure what else to do. If any has a similar experience or advice, please help! I don't want to stress her out anymore.