I think she doesn't understand how SEO works and is probably feeling you're not doing the job well. Or she could be trying to get you to do more work than she's willing to pay for by complaining. I suggest you don't do any more work but raise it up with the UPwork admin. You need to be careful with these freelance sites. Some of the job posters can be quite fraudulent. I've had to transcribe a whole 60 minutes audio before and the lady claimed I didn't meet the deadline and refused to pay. My rule is, don't take jobs that appear to be so much work, yet, has no clear terms of contract/project delivery. If possible, request a deposit before you begin. Tell them you'll need to pay for certain things for the job.

Hi AndrewFilm
I also just started up as a Freelance digital marketing professional and I'm still studying for my Msc in digital marketing. But, I have worked as a journalist for five years and I hold a BA in Mass Communication. These are my suggestions to help, based on my communication and marketing experience and knowledge. You may have done some already and this is not an exhaustive list.
1. You say you're already established so, I'm guessing you have a client base already and you already get a few jobs/projects. Do you have a website or an online channel like on Youtube? You might want to start your advertising thereby showcasing some of your work (with your client's approval) or demo of what you do.
2. You might want to consider promoting your brand on social media but first identify the social media channels your clients prefer to use. i.e, Facebook, Twitter, Youtube. etc
3.Invite your friends and clients to follow you and urge them to invite their own networks to follow your social channels and use those platforms to tell them about your services.
I seriously suggest you utilise your website well if you have one or consider getting a website if you don't. You can send me a direct message if you need more tips.
Cheers