QoS on a bridged modem when router itself doesn't have QoS

So.. This might be a bit of a silly question but I have limited knowledge of networking.
I'll try to keep it short..

I have a Zyxel AMG1001-T10A ADSL2+ modem and a Dovado 4GR router.
Modem is bridged and the router handles the internal network, WLAN and so forth.
Router itself doesn't have any sort of QoS features but otherwise I'm extremely pleased with it.
The modem on the other hand does have QoS. Here's pages 74-80 from it's manual which shows what it has.

QoS itself is already enabled out of the box on the modem but it is the extra options I'm interested in.
I don't know if having it enabled actually does anything without having any rules, at least when I use the DSLReports Jitter test, without downloading anything I get an average ping deviation around 1.5-1.55ms on my computer with this ADSL2+ connection but when I have a big download going the ping dev goes to 20ms.
Dear lord how much the ping dev goes up on the laptop when the ping dev without any extra network load is already above 10ms on the laptop. Ugh, WiFi.

I'd be interested if I could utilize the QoS features on the modem. In other words give higher priority to data from the laptop of the missus and lower priority for my computer.
Read maintain peace. She doesn't do big downloads or anything, just general browsing and online Minecraft so it would be nice that any dicking around I do online wouldn't impact her too much, like for example if I download a big file.

Is that possible? The modem is bridged so how would it know what is what when router does the internal network?
I've heard the terms tagging/marking before? Like, could I flip some switch on the laptop (Windows 8.1, Atheros wireless) so the modem would know what packets come from the laptop?

I'm not expecting a guide! But maybe a general or even a vague yes or no would probably be sufficient.
I could then go and research/learn how to do it and if I hit a wall I could then ask for help.

If no then I'll grudginly look into buying a new router with more features, even though the Dovado is otherwise perfect. Meanwhile I'll limit the download speeds or do them when she's not around :D

I am not super familiar with Zyxel products, or Dovado. Generally speaking you would turn qos on, and setup rules. Rules being IP specific or port specific. Also you would setup bandwidth minimums and maximums. For example, guarantee 20% of download traffic for port 80 and give it a maximum of 100% so anyone browsing the web would be guaranteed at least 20% of the bandwidth even if you were downloading something huge.

Many routers allow packet prioritization... I guess this is what you are referring to. This allows you to "tag" packets from specific ips or ports so that they take precedence over other packets. So you could tell your router to always give the laptop priority. The setup varies greatly from router to router.

You would really need to play with this on your own. The example in the manual has it setup for VOIP. Hopefully it will let you change that to blank and specify your own ports or go strictly by IP address. Try and setup a rule and run a speed test on both systems at once. The one with higher priority should come out on top. This is of course if you are going only off of ip address. If you are giving specific ports priority make sure you find a test that specifically uses that port.